Sucrose metabolism plays pivotal roles in development, stress response, and yield formation, mainly by generating a range of sugars as metabolites to fuel growth and synthesize essential compounds (including protein, cellulose, and starch) and as signals to regulate expression of microRNAs, transcription factors, and other genes and for crosstalk with hormonal, oxidative, and defense signaling. This review aims to capture the most exciting developments in this area by evaluating (a) the roles of key sucrose metabolic enzymes in development, abiotic stress responses, and plant–microbe interactions; (b) the coupling between sucrose metabolism and sugar signaling from extra- to intracellular spaces; (c) the different mechanisms by which sucrose metabolic enzymes could perform their signaling roles; and (d ) progress on engineering sugar metabolism and transport for high yield and disease resistance. Finally, the review outlines future directions for research on sugar metabolism and signaling to better understand and improve plant performance.

https://www.researchgate.net/profile/Yong-ling_Ruan2/publication/260441137_Sucrose_Metabolism_Gateway_to_Diverse_Carbon_Use_and_Sugar_Signaling/links/00b7d53ab58e606a20000000.pdf

Sucrose metabolism: gateway to diverse carbon use and sugar signaling.

MicroRNAs (miRNAs) are endogenous ∼23 nt RNAs that play important gene-regulatory roles in animals and plants by pairing to the mRNAs of protein-coding genes to direct their posttranscriptional repression. This review outlines the current understanding of miRNA target recognition in animals and discusses the widespread impact of miRNAs on both the expression and evolution of protein-coding genes.

MicroRNAs: Target Recognition and Regulatory Functions

Sugars have a central regulatory function in steering plant growth. This review focuses on information presented in the past 2 years on key players in sugar-mediated plant growth regulation, with emphasis on trehalose 6-phosphate, target of rapamycin kinase, and Snf1-related kinase 1 regulatory systems. The regulation of protein synthesis by sugars is fundamental to plant growth control, and recent advances in our understanding of the regulation of translation by sugars will be discussed.

/pdf/sugar-signals-and-the-control-of-plant-growth-and-u5xjaybmv4.pdf

Sugar signals and the control of plant growth and development

Plants are sessile organisms that gauge stressful conditions to ensure survival and reproductive success. While plants in nature often encounter chronic or recurring stressful conditions, the strategies to cope with those are poorly understood. Here, we demonstrate the involvement of ARGONAUTE1 and the microRNA pathway in the adaptation to recurring heat stress (HS memory) at the physiological and molecular level. We show that miR156 isoforms are highly induced after HS and are functionally important for HS memory. miR156 promotes sustained expression of HS-responsive genes and is critical only after HS, demonstrating that the effects of modulating miR156 on HS memory do not reflect preexisting developmental alterations. miR156 targets SPL transcription factor genes that are master regulators of developmental transitions. SPL genes are posttranscriptionally downregulated by miR156 after HS, and this is critical for HS memory. Altogether, the miR156-SPL module mediates the response to recurring HS in Arabidopsis thaliana and thus may serve to integrate stress responses with development.

/pdf/arabidopsis-mir156-regulates-tolerance-to-recurring-1o8iumb85k.pdf

Arabidopsis miR156 Regulates Tolerance to Recurring Environmental Stress through SPL Transcription Factors

Plants frequently have to weather both biotic and abiotic stressors, and have evolved sophisticated adaptation and defense mechanisms. In recent years, chromatin modifications, nucleosome positioning, and DNA methylation have been recognized as important components in these adaptations. Given their potential epigenetic nature, such modifications may provide a mechanistic basis for a stress memory, enabling plants to respond more efficiently to recurring stress or even to prepare their offspring for potential future assaults. In this review, we discuss both the involvement of chromatin in stress responses and the current evidence on somatic, intergenerational, and transgenerational stress memory.

/pdf/epigenetic-and-chromatin-based-mechanisms-in-environmental-8v9omdkdt7.pdf

Epigenetic and chromatin-based mechanisms in environmental stress adaptation and stress memory in plants.

The transition from the juvenile to adult phase in plants is controlled by diverse exogenous and endogenous cues such as age, day length, light, nutrients, and temperature. Previous studies have shown that the gradual decline in microRNA156 (miR156) with age promotes the expression of adult traits. However, how age temporally regulates the abundance of miR156 is poorly understood. We show here that the expression of miR156 responds to sugar. Sugar represses miR156 expression at both the transcriptional level and post-transcriptional level through the degradation of miR156 primary transcripts. Defoliation and photosynthetic mutant assays further demonstrate that sugar from the pre-existing leaves acts as a mobile signal to repress miR156, and subsequently triggers the juvenile-to-adult phase transition in young leaf primordia. We propose that the gradual increase in sugar after seed germination serves as an endogenous cue for developmental timing in plants.

https://cdn.elifesciences.org/articles/00269/elife-00269-v1.pdf

Sugar is an endogenous cue for juvenile-to-adult phase transition in plants

Plant cells are totipotent and competent to regenerate from differentiated organs. It has been known for six decades that cytokinin-rich medium induces shoot regeneration from callus cells. However, the underlying molecular mechanism remains elusive. The homeodomain transcription factor WUSCHEL (WUS) is essential for de novo establishment of the shoot stem cell niche in Arabidopsis thaliana We found that WUS-positive (WUS+) cells mark the shoot progenitor region during regeneration. A cytokinin-rich environment initially promotes the removal of the repressive histone mark H3K27me3 at the WUS locus in a cell cycle-dependent manner. Subsequently, the B-type ARABIDOPSIS RESPONSE REGULATORs (ARRs) ARR1, ARR2, ARR10, and ARR12, which function as transcriptional activators in the cytokinin signaling pathway, spatially activate WUS expression through binding with microRNA165/6-targeted HD-ZIP III transcription factors. Thus, our results provide important insights into the molecular framework for cytokinin-directed shoot regeneration and reveal a two-step mechanism for de novo activation of WUS.

/pdf/a-two-step-model-for-de-novo-activation-of-wuschel-during-1qzmy8efgb.pdf

A Two-Step Model for de novo Activation of WUSCHEL during Plant Shoot Regeneration

Plants flower in response to many varied cues, such as temperature, photoperiod, and age. The floral transition of Cardamine flexuosa, a herbaceous biennial-to-perennial plant, requires exposure to cold temperature, a treatment known as vernalization. C. flexuosa younger than 5 weeks old are not fully responsive to cold treatment. We demonstrate that the levels of two age-regulated microRNAs, miR156 and miR172, regulate the timing of sensitivity in response to vernalization. Age and vernalization pathways coordinately regulate flowering through modulating the expression of CfSOC1, a flower-promoting MADS-box gene. The related annual Arabidopsis thaliana, which has both vernalization and age pathways, does not possess an age-dependent vernalization response. Thus, the recruitment of age cue in response to environmental signals contributes to the evolution of life cycle in plants.

http://science.sciencemag.org/content/sci/340/6136/1097.full.pdf

Molecular Basis of Age-Dependent Vernalization in Cardamine flexuosa

Plant cells are totipotent and competent to regenerate from differentiated organs. It has been shown that two phytohormones, auxin and cytokinin, play critical roles within this process. As in animals, the regenerative capacity declines with age in plants, but the molecular basis for this phenomenon remains elusive. Here, we demonstrate that an age-regulated microRNA, miR156, regulates shoot regenerative capacity. As a plant ages, the gradual increase in miR156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors leads to the progressive decline in shoot regenerative capacity. In old plants, SPL reduces shoot regenerative capacity by attenuating the cytokinin response through binding with the B-type ARABIDOPSIS RESPONSE REGULATORs, which encode the transcriptional activators in the cytokinin signaling pathway. Consistently, the increased amount of exogenous cytokinin complements the reduced shoot regenerative capacity in old plants. Therefore, the recruitment of age cues in response to cytokinin contributes to shoot regenerative competence.

/pdf/an-intrinsic-microrna-timer-regulates-progressive-decline-in-4upflyfatc.pdf

Heng Lian

Papers

Sugar is an endogenous cue for juvenile-to-adult phase transition in plants

A Two-Step Model for de novo Activation of WUSCHEL during Plant Shoot Regeneration

Molecular Basis of Age-Dependent Vernalization in Cardamine flexuosa

An Intrinsic MicroRNA Timer Regulates Progressive Decline in Shoot Regenerative Capacity in Plants

Plant developmental transitions: the role of microRNAs and sugars